This application claims the priority benefit of Taiwan application serial no.91202654, filed Mar. 7, 2002.
1. Field of Invention
The present invention relates to a pressure control device. More particularly, the present invention relates to a pressure control device inside the ink reservoir of an inkjet module.
2. Description of Related Art
In general, the print head of an inkjet printer has some mechanism for controlling the flow of ink from an ink reservoir to print media. To prevent ink from leaking out of the print head, a partial vacuum is usually created inside the ink reservoir so that the air pressure inside the reservoir is slightly smaller than external atmospheric pressure. Hence, a negative pressure permanently exists inside the ink reservoir and leakage of ink is prevented. Note that if the negative pressure inside the reservoir is too high, the inkjet print head may not provide sufficient force to spread out the ink. Thus, the negative pressure inside the ink reservoir must be maintained within a definite range for normal operation of the print head.
However, due to constant fluctuation of atmospheric pressure, negative pressure inside the ink reservoir changes correspondingly. To maintain the negative pressure within a defined range, a number of pressure regulators have been developed. For example, one such pressure regulator for controlling the negative pressure inside an ink reservoir is disclosed in Taiwan Patent No. 438684 (U.S. Pat. No. 6,213,598).
FIGS. 1A and 1B are schematic cross-sectional views showing a portion of the internal layout of a pressure regulator as described in U.S. Pat. No. 6,213,598. As shown in FIGS. 1A and 1B, an air bag 136 is installed inside an ink reservoir 110. The air bag 136 is connected to the external atmosphere through a pipeline 138 so that internal volume of the ink reservoir 110 may increase or decrease by expanding or contracting the air bag 136. Ultimately, pressure inside the ink reservoir 110 also changes. Using this mechanism, negative pressure inside the ink reservoir is maintained within a permitted range. However, the air bag 136 must encounter a limit to expansion. When most of the ink inside the reservoir is used and the air bag has expanded so much that the negative pressure inside the ink reservoir is no longer regulated by the air bag 136, negative pressure inside the ink reservoir gradually rises. To bring down the negative pressure again, a pressure control device 200 is often fitted inside the ink reservoir 110 so that external gases may rush into the ink reservoir 110 to increase the gas pressure inside the ink reservoir 110. Hence, negative pressure inside the ink reservoir 110 is lowered and internal pressure is maintained within a permitted range.
As shown in FIG. 1A, the pressure control device 200 further includes a vent 210, a plugging block 220 and a spring-loaded structure 230. The vent 210 includes a hole 212 and a groove 214. The hole 212 is a connective channel linking up both the interior and the exterior of the ink reservoir 110. Furthermore, the groove 214 is at the upper end of the hole 212 while the plugging block 220 is placed inside the groove 214. A first section 230a of the spring-loaded structure 230 presses against the upper portion of the plugging block 220 so that the plugging block 220 seals the hole. Hence, the interior of the ink reservoir 110 is isolated from the exterior. The plugging block 220 can be a spherical body such as a steel ball. When the air bag 36 continues to expand and moves a plate 134 in the B direction, the plate 134 pushes against a second section 230b of the spring-loaded structure 230 as shown in FIG. 1B. In the meantime, such movement in the second section 230b of the spring-loaded structure 230 raises the first section 230a of the spring-loaded structure 230. Ultimately, the first section 230a of the spring-loaded structure 230 no longer comes in contact with the upper edge of the plugging block 220.
Since air pressure outside the ink reservoir 110 is greater than internal air pressure, an external pressure will exert on the plugging block 220 through hole 212 trying to raise the plugging block 220. This will increase the air pressure inside the ink reservoir 110 and lower the negative pressure that exists between the interior and exterior of the ink reservoir 110. The spring 132 of a pressure regulator 130 compresses the air sac 136 by exerting a force against the pressure plate 134 in direction A as shown in FIG. 1A. However, when the plate 134 no longer touches the second section 230b of the spring-loaded structure 230, the first section 230a of the spring-loaded structure 230 will return to an elastic state pressing against the upper edge of the plugging block 220. Consequently, the plugging block 220 returns to the original position sealing the nozzle hole at the upper end of hole 212 and restores the partition between the interior and exterior of the ink reservoir 110.
As shown in FIGS. 1A and 1B, the spring-loaded structure 230 of a conventional pressure control device 200 is a piece of metallic strip. When the pressure plate 134 of the pressure regulator 130 exerts too much pressure on the second section 230b or the ink module 100 vibrates too much, the first section 230a is raised to a high level moving the first section 230a away from the plugging block 220. Thus, the first section 230a is unable to hold the plugging block 220 in position any longer. Sometimes, the plugging block 220 may jump out of the groove 214 forever so that the nozzle 212 is no longer sealed. In other words, the pressure control device 200 no longer works in tandem with the pressure regulator 130 to provide necessary negative pressure adjustment inside the ink reservoir 110.
Accordingly, one object of the present invention is to provide a pressure control device capable of maintaining the negative pressure inside an ink reservoir within a definite range and limiting the moving range of an internal spring-loaded structure, in particular, the moving range of a first section of the spring-loaded structure so that the dislodging of a plugging block from functional position is prevented and pressure control is always maintained.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a pressure control device installed inside an ink reservoir. The pressure control device sets up a negative pressure between the interior and the exterior of the ink reservoir. The ink reservoir further includes a pressure regulator. The pressure control device at least includes a vent, a plugging block and a spring-loaded structure. The vent is positioned inside the interior wall of the ink reservoir. The vent has a groove near the upper end of the hole. The plugging block is placed within the groove for partitioning the ink reservoir into an interior and an exterior. The spring-loaded structure is also set up within the interior wall of the ink reservoir. The spring-loaded structure has a first section and a second section. The first section presses against the outer edge of the plugging block and exerts an elastic force on the plugging block. The second section is coupled to the pressure regulator so that any change in negative pressure is transformed into a corresponding movement of the second section of the spring-loaded structure. In this way, the first section of the spring-loaded structure is detached from the outer edge of the plugging block.
To prevent the first section of the spring-loaded structure from moving too far away from the plugging block so that the plugging block may jump out of the groove, the spring-loaded structure includes a third section connected to the second section of the spring-loaded structure. One end of the third section runs in a direction parallel to the movement of the pressure regulator and extends towards the interior sidewall of the ink reservoir yet is detached from the interior wall of the ink reservoir, thereby limiting the range of movement of the third section. Hence, the range of movement of the second section and the second section are also restricted.
Similarly, to prevent the first section of the spring-loaded structure from moving too far away from the outer edge of the plugging block and jumping out of the groove, a limiting structure may be set up somewhere along the moving trajectory of the first section of the spring-loaded structure. Hence, the first section of the spring-loaded structure is free to move within a definite range only.
By the same token, to prevent the first section of the spring-loaded structure from moving too far away from the outer edge of the plugging block and jumping out of the groove, the spring-loaded structure may further include an additional third section. The third section corresponds with another limiting structure inside the ink reservoir that confines the movement of the third section. Ultimately, the first section of the spring-loaded structure is free to move within a definite range only.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.